1. Field of the Invention
This invention relates to the production of 2-ethyl hexanal by hydrogenation of 2-ethyl hexene-2-al-1. It involves the discovery that the hydrogenation may be accomplished without producing 2-ethyl hexanol as a byproduct by using liquid phase upflow through a catalyst bed under controlled hydrogen concentration and reaction conditions.
2. Description of the Prior Art
Unsaturated carbonyl compounds can be produced on an industrial scale by aldolization processes, e.g., see U.S. Pat. No. 3,248,428. Dimerization of butyraldehyde in this manner followed by dehydration of the condensation product produces 2-ethyl hexene-2-al-1 (TEH). The present invention utilizes TEH prepared in this or any other manner for the production of 2-ethyl hexanal.
When unsaturated carbonyl compounds, e.g., .alpha.-.beta. unsaturated aldehydes, are hydrogenated either the olefinic unsaturation may be saturated, the carbonyl group may be reduced or both reactions may occur. For production of saturated carbonyl compound from the unsaturated analog there has been employed either catalytic liquid phase hydrogenation process (see U.S. Pat. No. 3,272,873) or vapor phase hydrogenation process that has strong activity for olefinic hydrogenation (see U.S. Pat. No. 3,278,605). Palladium catalysts are known to have a strong activity for hydrogenating olefinic unsaturation (see U.S. Pat. No. 3,280,192).
It is also known that the hydrogenation of the unsaturated carbonyl compounds may simultaneously produce saturated carbonyl compounds and saturated alcohol, e.g., 2-ethyl hexanal and 2-ethyl hexanol from TEH (see U.S. Pat. No. 3,449,435).
Although anhydrous, or substantially anhydrous, reaction systems are more generally employed in hydrogenations as outlined above, aqueous systems have also been disclosed as useful to saturate the olefinic group without reduction of the carbonyl function (see U.S. Pat. No. 3,185,757).
Palladium catalysts and other having selected activity for olefinic unsaturation hydrogenation are generally expensive and often subject to poisoning by trace impurities. Furthermore, processes designed to saturate the olefinic group in unsaturated carbonyl compounds without reduction of the carbonyl function frequently fail to produce high conversions to the desired product, even when selected activity catalysts are involved. Accordingly, there is a need, notwithstanding the state of development of the art, for improvements in the selective hydrogenation of unsaturated aldehydes to saturated aldehydes and, specifically, conversion of TEH to 2-ethyl hexanal.